L.B. Christie, P.J. Schneider, J.R. Heidrich, K.W. Oh
University at Buffalo,
Keywords: photoacoustics, test phantom
Summary:Photoacoustic (PA) research is an up and coming field that is being applied to the medical space. PA combines the use of both optics and acoustics to create a final outputted signal (Figure 1). The use of both of these technologies allows for a high depth penetration and signal resolution. Test phantoms are recreations of the human body that allow for a consistent and accurate measurements on a modality. The benefit to using a test phantom is that they are comprised of known parameters producing signals that are “expected”. This is a property that is not common in the human body from day to day. A test phantom was created with equivalent PA response to the human body and measured through the use of PA. An image of the test phantom can be seen in Figure 2. Prior Work: PA phantoms have been created to recreate a human finger signal . Depth of the channels and channel size could be predicted through ultrasonic equations. Many similarities between the phantom signal and the human signal were observed such as the amplitude of the signal and the shape of the heart rate waveform. Methods: PA test phantoms were comprised of a few main components, tissue, blood, phantom pump, arteries / veins, and a shell. The phantom tissue was comprised of polydimethylsiloxane (PDMS), a clear silicone rubber. This material allows for a similar hardness and modulus to that of human tissue. Arteries and veins were created through the implanting of a water-soluble 3D printing material known as polyvinyl alcohol (PVA) in PDMS at specific depths. This was done using solder clamps holding thin square wires of PVA until PDMS was cured, see Figure 3. This allowed for specific channel depths to be implemented into the phantom itself, while also allowing channels to be angled for any needed application. A PA blood simulant made up of glycerin, water, and black ink was made to mimic human blood. A shell providing support and structure to the rubber phantom was also made using aluminum milled to a specific size. Finally, a Gampt M2 pump was implemented to pulse human heart rate waveforms through the phantom channels . A final image of the test setup can be seen in Figure 4. Experimentation and Results: Utilizing the test setup that is shown in Figure 4, phantoms were placed on a PA testbench with a 532nm laser wavelength and data was captured. A “artery like” waveform was pulsed through the phantom with the Gampt M2 pump. This waveform was meant to closely mimic the pressure and shape of the human artery heart rate waveform. A PA signal over time was collected. A comparison between the inputted signal and the outputted PA signal can be seen in Figure 5. The outputted PA signal maintained a similar shape to that of the inputted signal. The amplitude of the signal could be adjusted by changing the pump pressure and the concentration of PA ink that is used in the phantom itself.